This invention is concerned with organic compounds which are useful as pharmaceutical agents. The compounds of the present invention are 1-piperazinethiocarboxamides which are capable of ameliorating atherosclerosis in mammals. The invention further relates to novel 1-piperazinethiocarboxamides and methods for the chemical synthesis of these compounds. The invention also relates to pharmaceutical compositions for the utilization of these compounds in the treatment of disease in mammals. The invention contemplates methods for treating atherosclerosis in a mammal in a manner designed to prevent, arrest, or reverse the course of the disease.
The specific compounds of this invention are 4-heteroaryl-1-piperazinethiocarboxamides and this invention contemplates as novel compounds per se only certain types of 4-heteroaryl-1-piperazinethiocarboxamides which are not known in the art. Four 4-(2-pyrazinyl)-1-piperazinethiocarboxamides have been described (Chem. Abstr. 49, 384d and 11666b); however, there is no known report of antiatherosclerotic activity for these compounds.
Atherosclerosis is a form of arteriosclerosis characterized by lipid accumulation in and thickening of the arterial walls of both medium and large-sized arteries. Arterial walls are thereby weakened and the elasticity and effective internal size of the artery is decreased. Atherosclerosis is the most common cause of coronary artery disease and is of great medical importance since the occlusion of medium and large-sized arteries diminishes the supply of blood to vital organs such as the heart muscles and the brain. The sequelae to atherosclerosis include ischemic heart disease, heart failure, life-threatening arrythmias, senility and stroke.
The fact that cholesterol is a major component of atherosclerotic lesions or plaques has been known for more than 100 years. Various researchers have studied the role of cholesterol in lesion formation and development and also, more importantly, whether lesion formation can be prevented or lesion development arrested or reversed. Atheromatous lesions have now been shown [Adams, et al., Atherosclerosis, 13, 429 (1974)] to contain a greater quantity of esterified as opposed to unesterified cholesterol than the surrounding undiseased arterial wall. The intracellular esterification of cholesterol with fatty acids is catalyzed by the enzyme "Fatty acyl CoA:cholesterol acyl transferase" or ACAT and the accumulation and storage of cholesterol esters in the arterial wall is associated with increased activity of this enzyme [Hashimoto and Dayton, Atherosclerosis, 28, 447 (1977)]. In addition, cholesterol esters are removed from cells at a slower rate than unesterified cholesterol [Bondjers and Bjorkerud, Atherosclerosis, 15, 273 (1972) and 22, 379 (1975)]. Thus, inhibition of the ACAT enzyme would diminish the rate of cholesterol esterification, decrease the accumulation and storage of cholesterol esters in the arterial wall, and prevent or inhibit the formation and development of atheromatous lesions. The compounds of the present invention are very potent inhibitors of the ACAT enzyme. Thus, these compounds are useful for controlling and reducing the cholesterol ester content of mammalian arterial walls and decreasing the accumulation and storage of cholesterol in the arterial walls of mammals. Further, the compounds of this invention inhibit the formation or development of atherosclerotic lesions in mammals.
The evidence that hyperlipidemia is one of the factors involved in coronary heart disease is very impressive. A most important study carried out in Framingham, Mass. (Gordon and Verter, 1969) in over 5,000 persons for more than 12 years established a correlation between high concentrations of blood cholesterol and increased risk of heart attack. Although the causes of coronary artery disease are multiple, one of the most constant factors has been the elevated concentration of lipids in the blood plasma. A combined elevation of cholesterol and triglycerides has been shown (Carlson and Bottiger, 1972) to carry the highest risk of coronary heart disease. The majority of patients with ischemic heart disease or peripheral vascular disease were found to have hyperlipoproteinemia, involving very low-density and/or low-density lipoproteins (Lewis, et al., 1974).
We have now found that certain members of this class of compounds can safely and effectively lower serum lipids in warm-blooded animals. Such action on serum lipids is considered to be very useful in the treatment of atherosclerosis. For some time it has been considered desirable to lower serum-lipid levels and to correct lipoprotein imbalance in mammals as a preventive measure against atherosclerosis. The compounds of the present invention do not act by blocking late stages of cholesterol biosynthesis and thus do not produce accumulation of intermediates such as desmosterol, as equally undesirable as cholesterol itself. Compounds with the combination of therapeutically favorable characteristics possessed by those of the present invention can be safely administered to warm-blooded mammals for the treatment of hyperlipidemic and atherosclerotic states found in patients with or prone to heart attacks, to peripheral or cerebral vascular disease, and to stroke.
The compounds of this invention exhibit antiatherosclerotic activity and the invention should not be construed as limited to any particular mechanism of antiatherosclerotic action.